Coating composition for subbing polystyrene film



United States Patent 3,168,408 CQATING COMPGSITION FOR SUBBING POLYSTYRENE FHLM Jay J. Uber, South Hadley, Mass, assignor to The Plastic Coating Corporation No Drawing. Filed Sept. 18, 1961, Ser. No. 138,567

. 8 Claims. (Cl. 106-128) This invention relates to a coating composition for use in the production of a photographic film having a polystyrene base sheet.

Polystyrene film has heretofore been proposed for use as a photographic film support and is finding increasing commercial use for this purpose. A serious problem has heretofore been presented in securing a firm bond between the surfaces of a polystyrene base sheet and the light-sensitive coating of a gelatin-silver halide emulsion. Various solutions have been proposed for the solution of this problem.

One proposed solution has been the application of an intermediate subbing layer consisting of two or more coatings of different compositions. This solution to the problem has the disadvantage of requiring two or more coating operations to form the subbing, prior to the application of the light-sensitive coating, thereby increasing the cost of the product.

Another solutionto the problem has involved the substitution of a special light-sensitive coating for the conventional gelatin-silver halide emulsion. This solution to the problem has the dual disadvantage of requiring a material and complex deviation from the normal procedures for the application of the conventional gelatinsilver halide emulsion coatings, with increased cost arising both from the more expensive ingredients used in the special light-sensitive coating composition and the complex procedure involved in the formulation of the light-sensitive coating composition. A third solution to this problem has involved a combination of the foregoing alternative solutions Which combines the economic disadvantages of each of those alternatives.

Specific examples of each of these alternative solutions to this problem are described by U.S. 2,816,027, issued December 10, 1957, to Thomas H. Farrell et a1. While describing in considerable detail these alternative solutions to the problem, that patent states that for certain purposes it is not necessary to apply a subbing to polystyrene sheeting before coating it with a photographic emulsion, especially where the photographic film is to be employed at comparatively high relative humidity. However, as a practical matter, the application of a subbing coating to a polystyrene base sheet is essential in the production of photographic film intended for any normal usage.

It will be understood that the term subbing is used in this specification in its usually accepted sense to mean an intermediate film or coating on the surface of a base sheet or film which bonds a photographic gelatin-silver halide emulsion to the surface of the base sheet or film.

In my copending U.S. patent application, Serial No. 826,433, filed July 13, 1959, which matured into U.S. 3,010,838, and, of which this application is a continuation-in-part, I have disclosed a coating composition for application to a polystyrene base sheet or film in a single coating operation to form a subbing which Will receive 3,158,408 Patented Feb. 2, 1965 mixture of cresols, and acetic acid dispersed in a suitable volatile solvent for nitrocellulose. It may contain about 0.5% to about 2.0%, by weight, ofgelatin and preferably contains an amount within the range of about 0.75%, to about 1.5%, by weight. It may contain an amount of nitrocellulose within the range of about 0.25% to about 2.25%, by weight, and preferably within the range of about 0.75%, by weight, to about 1.5%, by weight. It will contain an amount of phenol within the range of about 1.0% to about 5.0%, by weight, and preferably 2.0% to about 4.0%, by weight. The acetic acid content of the compositionmay be within the range of 1.5% to about 6.0%, by Weight, and preferably will be within the range of about 2.0%, to about 4.0%, by weight.

A substantial proportion of the phenol, cresol or the mixture of cresols in this composition appears to remain in the coating film after the evaporation of the volatile solvents therefrom and increases the adhesion of the coating film to the surface of the polystyrene sheet or film. Although this composition is a definite advance in the subbing of polystyrene sheets or films, it has the disad vantage or producing a product which has a residual odor of phenol or cresol, as the case may be. Further, its preparation and use in the coating of the polystyrene film or sheet involves the hazard of handling phenol, cresol or the mixture of cresols, which are inherently dangerous chemicals. i

I have found that a coating composition which is adapted for application to a polystyrene sheet or film in a single coating operation to form a subbing which will receive and firmly bond a conventional light-sensitive gelatin-silver halide coating to the polystyrene base sheet or film, which is a definite improvement over the composition disclosed by my copending application, Serial No. 826,433, may be prepared by the substitution of a liquid low molecular weight styrenated-phenol polymer for all or a significant part of the phenol, the cresol or the mixture of cresols in the coating composition of that copending application.

The coating. composiiton in accordance with this invention comprises gelatin, nitrocellulose, liquid low molecular weight styre'nated-phenol polymer and acetic acid dispersed in a suitable volatile solvent for nitrocellulose. It may contain about 0.5% to about 2.0%, by Weight, of gelatin and preferably contains an amount Within the range of about 0.5 to about 1.5 by weight. It may contain an amount of nitrocellulose within the range of about 0.25 to about 2.25 by weight, and preferably within the range of about 0.75%, by Weight, to about 1.5 by weight. It will contain an amount of styrenated phenol within the range of about 0.5%, by Weight, to about 3.5%, by Weight. The acetic acid content of the composition maybe within the range of 1.5% to about 6.0%, by weight, and preferably will be within the range of about 2.0% to about 4.0%, by weight. The acetic acid in this composition acts as a solvent for the gelatin therein and permits its solution in the anhydrous solvent for the nitrocellulose. It is a volatile constituent of the composition. i

The remainder of this composition consists essentially of a volatile solvent for the particular type of nitrocellulose which is included in the composition and is preferably a volatile solvent mixture for the nitrocellulose Which includes toluene as a volatile non-solvent diluent in the mixture. The toluene in the volatile solvent mixture appears to have a definite action in improving the adhesion of the film deposited by the composition of the polystyrene sheet or film. The formulations of suitable volatile solvent mixtures for the conventional types of nitrocellulose; which; are includedin this,composition are: well known tothe prior art.

The liquid-low; molecular weight styrenated phenolpolymerwhich forms an essential component of my 1mproved; compositionis a; polymerizedr alkylaryl phenol. Acomrnercial product identifiedbythetrademark Wing- Stay S? is entirely suitable for use inthis composition. The physical properties of" Wing-Stay S are. given in a leL The-viscosityof this polymer is an index-of the extentoii its I polymerization. I

Itis. a well-recognized. fact;that the-strength of nitrocellulose varies with its viscosity characteristic withthe strength vfalling ofirapidly. with the lower viscosity types. Despite this well-known;fact,;1 have found inthe caseof a subbing film deposited from the comp osition;of;this invention, that. itsbonding strengthincreases whenthe lower viscosity types of nitrocellulose, are used inthe composition, A. nitrocell.ulose: having a viscosity characteristic of 15 seconds gives very poor adhesion between a photographic gelatin-silver halide emulsion filmand a polystyrene surface. Itis desirable touse, a nitrocellulose in this. coating composition vwhich hasa. viscosity characteristic within therange. of. aboutlO centipoisesto about 5 seconds, and Iv prefer to use a; nitrocellulose having a viscosity characteristic of within the range. of about centipoises to about /2 second. A -centipoise, nitrocellulose has beenfound. to give excellent results; in this composition. The, viscosity characteristic. of a nitrocellulose of a type higher than 1A second maybe measured by the standard falling ball method described by ASTM specification D301-50, while viscosity. characteristics of A; secon d;or lower can be conveniently measured-by the, use of a capillary viscometerdescribed, for example, on page ofthe Hercules,Nitrocellulose Handbook, publishedjby Hercules PowdenCompany. The .nitro.cel-. lulose may be of the, RS type (11.8, to 12.2% nitrogen or of the SSjtype (10.9 to 11.2% nitrogen).

The polystyrene which is subbed, by. the, use. of the compositionofthis invention to. form the basesheetor film of a photographic film .is. ofjthe flexible type. which may be produced-by methods known in the art; U.S. Patent 2,074,285; issued-Mar. 16, 1937, to E. Studt'et al.', disclosesa--method for theproduction of such" sheets. The polystyrene sheet" or film may be of-anydesired thickness and 'will-usuallyhave-a thickness within the range of about 0.002jinch ro-0:020 inch.

The photographic silver halide. emulsion which is applied over the. subbing onthe-polystyrene is of the -,c.0l1- n ional a yp ypic l p o ographic l en i e m -i sions include -si lver;chloride,- silver; bromide, silver iodide, silver bromiodide, silver chlorobromide and silver chlorobromiodide emulsions. The carrier for the silvery halide is gelatin.

The coating composition in accordance with this invention is specifically illustrated by the following example:

EXAMPLE I Gelatin 0.93 Glacial acetic acid 3.54

Toluene 5.22 n-Butyl alcohol 8.80 Nitrocellulose, 18 cps. (70%) 2.06 Acetone 1.67

Ethanol 0.15

Butyl acetate 0.17 Methanol 74.28

Phenol -7. Liquidstyrenated phenolpolymer 3.18

The composition illustrated by Example I may be applied to polystyrene filmin an .amount within the range of about-.6.5 lbs. to about. 16.5 lbs. (wet coating weight) per thousand square feet and preferably within the. range,

of-abouhSlbs. to aboutv 10 lbs. (wet coating weight) per thousand square feet.

Aswill be understood from the foregoing, the amounts of. gelatin, ofnitrocellulose, of: glacial acetic acid and of the liquidstyrenated phenolpolymer shown by. Example. Imay be varied. Ingeneral, the. ratio of nitrocellulose to gelatin. should be within the range of about 0.5 to parts by weight for each part by weight ofgelatin. Table II, gives ranges of proportion which may beused in the coating composition.

TABLE II Rangesof proportionsof ingredients for coating composition for; subbing polystyrene Percent-by wt.-

Gelatin 0.50-1.50 Nitrocellulose (viscosity with therangeof 10 centipoises-toMr-second) 0.25-2.25

Glacial-aeetic-acid 1.50-6.00

Liquid styrena-ted' phenol polymer 0.5-3.5

Volatile solventmixturw The remainder In ,the range of. compositions shown by Table II, no

3 phenol, cresols or mixturesof cresols are included in the composition. As already noted .hereinbefore, the liquid low molecular weightstyrenated Phenol polymer may be useclias a .replacernentfor all or a part of the phenol; the cresolorthe mixture. of cresolsin the coating composition of my copendingapplication, SerialNo. 826,433. To obtain, the beneficial action of the liquid styrenated phenol polymer inimprovingthe bonding strength, it is desirable-muse at.least;0. 1% and, preferably, 0.5%, by weight, as a replacement for a portion. of, the phenol, cresol or mixtureofcresols. In general, one part ofthe liquid low molecular weightj'styrenated phenol polymer is as effect ve as two parts by weight ofthe phenol, cresol or mixture of cresols, but no morethan 3.5% ofrthe liquid low molecular weightstyrenated phenolpolymer should be. included in the. composition since a higher proportion will soften ,the polystyrenebase film. Therefore,.an amountof phenol, cresolor mixture of cresols within the range of 0.9%, by weight, to 4.9%, by weight, maybe used, with. an amount of .theliquid low molecular weight. styrenated phenol; polymer within the range. of 0.1%, by weight, to, 3.5%., by weight. Preferably, an amount: otthev liquid low molecular. weight styrenated phenolpolymer within therange of ;0.5%,.by weight,- to 3.5 %,.byweight, is used in .a mixture, withanhamount of phenohcresolhor amixture of cresols within the range of. 0.5%, by Weight, to.4.5%,,by weight, The cresol which may beused, in this mixture maybe ortho cresol, meta c esol, para ,cresol. or. a mixture thereof.

When applied to .thesurface of a polystyrenesheet or film, the coating composition in accordance with this invention deposits a subbing coating which has definitely stronger adhesion to the surface of the polystyrene than those deposited by the prior art subbing compositions. This subbing coating has even stronger adhesion to the surface of the polystyrene sheet or film than that of the subbing coating deposited by the coating composition described by my. copending application, Serial No. 826,433. The improved adhesion of the subbing coating deposited by a representative composition of this invention as compared with those deposited by a representative prior art coating composition and by a coating composition representative of those described by my copending application is illustrated by the comparative tests described below.

Coating compositions having compositions given by Table III were applied evenly over the surface of sheets of polystyrene film in an amount equivalent to 8 to 10 lbs. of the solutions per thousand square feet of film. The sheets of film coated with these compositions were then dried for three minutes at 160 F. in a circulating hot air oven.

TABLE III Coating compositions for subbing polystyrene film used for comparative tests of the adhesion of the coating deposited therefrom for a polystyrene surface Example Example Example I II III Gelatin 0. 93 0. 93 O. 93 Glacial Acetic Acid 3. 54 3. 54 3. 54. Toluene 430+ 92 5. 22 5. 22 5. 22 n-Butyl alcohol 8. 80 8. 80 8. 8O Nitrocellulose18 cps 2. 06 2.06 2.06 1. 67 l. 67 1. 67 0. 0. l5 0. l5 Butyl Acetate 0. 17 0. 17 0. 17 Methanol 74. 28 74. 28 74. 28 Phenol 3. 18 Liquid styrenated Phenol P0lymer 3.18

As already noted, Example I is representative of the coating compositions of this invention. Example 11 is representative of those disclosed by my copending application, Serial No. 826,433, while Example HI is a representative prior art coating composition for subbing polystyrene film.

Each of the sheets of polystyrene film coated by the compositions of Examples I, II and III were dipped into an aqueous solution of a green dye for three minutes and the adhesion of the coating for the surface of the polystyrene film tested by the application of a six inch strip of Scotch brand cellophane tape to the surface of the coating which was then removed by a sharp jerk. The adhesion of the coating for the surface of the polystyrene film was rated as poor if all or most of the coating was removed from the polystyrene surface by the Scotch brand cellophane tape. The adhesion was rated as fair if a portion, but not all, of the coating was removed by the Scotch brand cellophane tape. The adhesion was rated as good if none of the coating was removed by the Scotch brand cellophane tape.

In these comparative tests, the coating deposited from the composition of Example I received a rating of good. The coating composition deposited by the coating composition of Example II was rated as fair, while that deposited from the composition of Example III was given a rating of poor.

In the foregoing, various details have been given to fully explain the nature of this invention. However, it will be fully understood that various changes and modifications can be made in those details without departing from the spirit of this invention or the scope of the claims which follow.

I claim:

1. A coating composition consisting essentially of about 0.5%, by weight, to about 2.0%, by weight, of gelatin;

about 0.5%, by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than 5 seconds as measured by the standard method ASTM Specification D30150; about 1.5% by about 6.0%, by weight, of acetic acid; about 0.5%, by weight, to about 3.5 by weight, of a liquid low molecular weight styrenated phenol polymer and a volatile organic solvent for said nitrocellulose.

2. A coating composition consisting essentially of about 0.5%, by weight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than /2 second as measured by the standard method ASTM Specification D30l-50; about 1.5% by about 6.0%, by weight, of acetic acid; about 0.5%, by Weight, to about 3.5%, by weight, of a liquid low molecular Weight styrenated phenol polymer and a volatile organic solvent for said nitrocellulose.

3. A coating composition consisting essentially of about 0.5%, by weight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than 5 seconds as measured by the standard method ASTM Specification D301-50; about 1.5% by about 6.0%, by weight, of acetic acid; about 0.5%, by weight, to about 3.5%, by Weight, of a liquid low molecular weight styrenated phenol polymer and a volatile organic solvent for said nitrocellulose which is a mixture containing toluene as a non-solvent diluent.

4. A coating composition consisting essentially of about 0.5%, by weight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than /2 second as measured by the standard method ASTM Specification D30l50; about 1.5 by about 6.0% by weight, of acetic acid; about 0.5 by weight, to about 3.5%, by weight, of a liquid low molecular weight styrenated phenol polymer and a volatile organic solvent for said nitrocellulose which is a mixture containing toluene as a non-solvent diluent.

5. A coating composition consisting essentially of about 0.5%, by weight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than 5 seconds as measured by the standard method ASTM Specification D30l-50; about 1.5% by about 6.0%, by weight, acetic acid; about 0.1%, by Weight, to about 3.5 by Weight, of a liquid low molecular weight styrenated copolymer; about 0.9%, by weight, to 4.9%, by weight, of a material selected from a group consisting of phenol, ortho cresol, meta cresol, para cresol and a mixture of cresols and a volatile organic solvent for said nitrocellulose.

6. A coating composition consisting essentially of about 0.75%, by weight, to about 2.0%, by weight, of gelatin; about 0.75%, by weight, to about 1.5%, by weight, of nitrocellulose having a viscosity characteristic of no higher than /2 second as measured by the standard method ASTM Specification D30l-50; about 2.0%, by Weight, of acetic acid; about 0.5%, by weight, to about 3.5%, by weight, of a liquid low molecular weight styrenated phenol polymer and a volatile organic solvent for said nitrocellulose which is a mixture containing toluene as a non-solvent diluent.

7. A coating composition consisting essentially of about 0.5 by weight, to about 2.0%, by weight, of gelatin; about 0.5 by weight, to about 2.25%, by weight, of nitrocellulose having a viscosity characteristic no higher than /2 second as measured by the standard method ASTM Specification D30l50; about 1.5% by about 6.0%, by weight, of acetic acid; about 0.5 by Weight, to about 3.5%, by Weight, of a liquid low molecular weight styrenated phenol polymer; about 0.5% to about 4.5% of a material selected from the group consisting of phenol, ortho cresol, meta cresol, para cresol and mixtures of cresols, and a Volatile organic. solvent forsaid nitrocellulose.

8. Acoating composition consisting essentially of. about 0.5%, by weight, toabout 2.0%, by weight, of gelatin; about 0.5%,..by. Weight, to about 2.25%, by Weight, of nitrocellulose having a viscositycharacteristic no higher than /2- secondasmeasured by. the standard methodof phenol, ortho'cresol, meta cresol, para cresol andmixtures of cresols, and a volatile organic solvent for said nitrocellulose which-isa mixture containing toluene as a non-solvent diluent.

References Cited in the file of this patent UNITEDSTATES PATENTS 822,107 Findlay May 29, 1906 2,341,877 Middleton et a1. Feb. 15; 1944 2,544,237 Reese Mar; 6, 1951 2,816,027 7 Farrel et' a1. Dec. 10, 1957 2,872,318 Starck- Feb. 3, 1959 

1. A COATING COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 0.5%, BY WEIGHT, TO ABOUT 2.3%, BY WEIGHT, OF GELATIN; ABOUT 0.5%, BY WEIGHT, TO ABOUT 2.25%, BY WEIGHT, OF NITROCELLULOSE HAVING A VISCOSITY CHARACTERISTIC NO HIGHER THAN 5 SECONDS AS MEASURED BY THE STANDARD METHOD ASTM SPECIFICATION D301-50; ABOUT 1.5% BY ABOUT 6.0%, BY WEIGHT , OF ACETIC ACID; ABOUT 0.5%, BY WEIGHT TO ABOUT 3.5%, BY WEIGHT, OF A LIQUID LOW MOLECULAR WEIGHT STYRENATED PHENOL POLYMER AND A VOLATILE ORGANIC SOLVENT FOR SAID NITROCELLULOSE. 